Nitric oxide (NO) is a serious atmospheric pollutant readily formed when fuels are combusted with any oxidant containing oxygen and nitrogen. Minimization of NO production has become a key goal of current combustor development.
To date, such efforts have relied on measurements of the total quantity of NO exiting a combustor or on measurements of local NO concentrations within the combustion volume. The gross measurement has the advantage of being relatively simple but provides no direct data on the spatial distribution of NO formation in the combustor. On the other hand, sampling as a function of position reveals the spatial distribution of NO concentration but the available implementations--intrusive sampling probes or laser-based optical sampling--are less-than-ideal for combustor development work. Intrusive probes perturb flow through the combustion volume and are subject to problems related to premature degradation of the sample, and furthermore each probe provides data for only one location at a time. Laser-based optical sampling requires a sophisticated and complex optical system, as well as open optical access to the combustion volume.
Their other strengths and weaknesses aside, both the gross and local types of measurement show only the instant quantity of NO present, which is a result of the entire previous combustion history of the gas sample examined. Neither approach is capable of indicating the local rate of NO formation, a parameter critical to intelligent refinement of combustor design.